Cause of Arcing inside a Medium Voltage Arc-Resistant Metal-clad Switchgear Compartment on a sunny day without any Evidence of Switching Surge

This paper describes what caused phase-phase arc fault in the cable compartment of a medium-voltage (MV) arc-resistant metal-clad switchgear without any evidence of external switching surge on the power system. Switchgear fault occurred on a sunny day to activate overcurrent protection relay to clear the fault instantaneously. After the arc fault incident, maintenance crew along with technical staff noted insulation damage was caused by signs of moist air and dust particles which led to insulation tracking to cause phase-phase arc fault. Air entry with dust particles and moisture was observed from the operation of arc-blast louver above the arc-exhaust chamber which has been opening and closing. Every time louver opens and closes some air will trap and go inside the cable compartment, which is against the basic design requirement of arc-resistant enclosure. Basic characteristics of arc-pressure increase and decrease (when arc-blast move through the arc exhaust chamber and louver) is included in the paper to understand important design requirements: ‘‘no outside air is allowed to go inside the arc-exhaust chamber.’’ Lessons learnt from this electrical incident, maloperation of arc-exhaust louver will require design modifications and proper coordination with the manufacturer of the arc-resistant chamber at arc-resistance switchgear. Papers ends with design recommendations for an arc-resistant switchgear application in inclement weathers and no outside air should get into the arc-exhaust chamber coming inwards from hinged flaps at the arc-resistance switchgear.

I. Introduction

Fig. 1, shows outdoor metal-clad arc-resistant (15 kV Class) 12.47 kV nominal switchgear voltage which suffered phase-phase fault inside the cable compartment without any switching surge on a clear sunny day when there was no evidence of external switching surge on the entire overhead and underground distribution system for the airport arc-resistant switchgear. Some arc took place from phase to grounded enclosure as phase-phase fault took placed before it was cleared by sensitive protection scheme at the breaker. This paper describes cause of arcing fault in the cable compartment within of the arc-resistance enclosure of the arcresistance switchgear. Switchgear enclosure with individual draw-out circuit breaker compartments were manufactured by a reputed company per the industry standards IEEE/ANSI [1] [2]. Insulated buses and cable terminations in individual compartment including arc-exhaust chamber to exhaust arc fumes vertically was cleared without shattering the switchgear enclosure. Thus, switchgear design fully met industry standards to be arc-resistant switchgear with the exception that the design of hinged flaps not suitable for inclement weather at airport near the San Francisco/Oakland Bay seen in Fig. 1.. Fig. 1

Switchgear located in the airport parking lot